🎯 Objectives
To familiarize the students with the:
- Process of homeostasis 🔄, the biological systems 🧬
- The brain modulation of these systems 🧠
- And how the body's systems can compete with each other for the survival of the organism 🛡️
- Brain and motivational states 🎭
- Homeostasis ⚖️, include temperature regulation 🌡️, Hunger 🍽️, thirst 💧, bio-rhythms ⏰, Sleep and awakening 😴⏰
- Pathology related to sleep cycles ⚠️
- Sleep disorders and treatment 🩺
⚖️ Homeostasis
Homeostasis: A balance and an optimal functioning system of the body have to be maintained for survival of the organism 🛡️. Therefore, there are well defined and, in most cases, autonomous neurological feedback systems 🔄 which work to maintain an internally stable environment of living organism 🧬.
📡 Feedback and Feed-Forward Systems
There are feed forward systems ⏩, feedback systems 🔄 that are constantly monitoring and informing each other of the status (think of very efficient information systems of the computer or an organization 💻) the brain areas and organs are kept informed of each other's status 🧠📊.
For example, the somatosensory systems 👐- the skin sensors send temperature information to the receptors in the brain 🌡️🧠 and the temperature receptors would send out messages for making appropriate adjustments 📡. However, the receptors do not exist only on the outside but also within the brain 🧠.
"It is only against a homeostatic background that other more active systems can function, and many of an animals activities are motivated by the homeostatic needs," 🎭 (Bridgeman 1988, p 237) 📚.
Homeostasis has evolved to support survival by maintaining optimal functioning ⚡, if any problems the whole system needs readjustments 🔧. If these are minor the systems would sustain it and make the changes ✅, however, if major changes are required and cannot be made these may lead to death 💀.
🎯 Motivated Behaviors
Actions and behaviors are motivated by the homeostatic requirements (which are signals of the body's needs) 📡. Behaviors are programmed to respond to the needs of homeostasis and motivated drives 🎭.
There are internal receptors 🧬, external receptors/stimuli 🌍, brain mechanisms 🧠, neurochemical regulatory systems 🧪 and these are all well synchronized ⚙️. During the process of evolution receptors evolved for specialized functioning such as for:
- Temperature regulation 🌡️
- Hunger 🍽️ (and nutrient, glucose, fat monitoring 📊)
- Thirst 💧 (fluid and salt levels 🧂)
- Sleep 😴 (awakening and sleep need ⏰)
We will discuss these four in detail 📚.
🌡️ Temperature Regulation
Temperature regulation is a motivated behavior in that it has all the important characteristics of motivated behaviors- According to Mogensen (1980) 👨🔬 temperature regulatory behavior is:
- Purposive 🎯 (the goal to warm or cool the body 🌡️)
- Persistent 💪 (behavior would continue till the goal has been reached ✅)
- Has periodicity ⏰ (winters nest building 🏠, fur or hibernating 😴)
- Prioritized 📊
Temperature regulation is a fairly well-defined system 📋 and the evolution of human temperature system is quite well laid out (and so it is in other animals) 🧬. This is an important evolution for maintaining optimum body functioning ⚡. As the evolution of varied species took place on land and sea 🌊, tropics or Iceland ❄️, Equator or the Poles 🌍 emerged the development of a strong and sensitive thermoregulatory system for their needs became necessary for survival 🛡️.
🦎 Ectotherms
Ectotherms: Amphibians 🐸, Reptilians 🦎 depend on their external environment for temperature regulation 🌍. These animals are not cold blooded but adjust by relocating to an environment 🏃. These may be called solar powered animals ☀️, who gain heat from the sun and solar heated places 🌞.
However, they cannot remain in places which are too hot 🔥 or too cold ❄️ (if too hot outside, they burrow holes and stay in those holes 🕳️, if too cold they come out in the sun ☀️). These animals have also evolved vasoconstrictors 🔵 and vasodilators 🔴 on the skin (vasoconstrictors contract blood vessels so less energy needed to be expended ⚡⬇️). The animals remain in a state of stupor in the cold 🥶—not very efficient workers with this state 💤.
🔬 Laboratory Example
In a laboratory in the US where I worked 🇺🇸, lizards 🦎 used in an experiment were anesthetized by keeping them in ice ❄️, and surgery could be carried out 🩺- and when warm 🌡️ they would come out of this state ⚡. This kind of a response in the amphibians and the reptilians is directly controlled by the thermoregulatory receptors in the hypothalamus 🏥 and the brain 🧠 and is dependent on the environment 🌍.
🔥 Endotherms
Endotherms: Mammalians 🦁 and birds 🦅 have evolved an effective temperature control system ⚙️- a set point around which the body functions like the thermostat of air conditioner or oven 🌡️. The endotherms have their own internal controls 🎛️.
🎯 Set Point
Set point: An internal point: temperature or standard that the body functions to maintain by cooling or heating through homeostasis (increase or decrease metabolism) 🌡️⚖️.
There is a neutral zone range around the set point within which the internal temperature can vary a few degrees higher or lower but not more than that 📊. If the temperature rises or drop beyond the range (more or less) ⚠️ than the thermo regulatory mechanisms for cooling or heating are activated and the metabolism works to meet the required (heat up or cool the body) 🔥❄️.
💪 Advantages of Endothermy
Because of their regulatory capacities 🎛️, the mammalian species and birds can manage continued activity for longer periods as compared to reptile 🦎 (when faced with the temperature challenges). Higher activity and metabolism challenges can be sustained ⚡—have a higher threshold 📈.
🌍 Environmental Adjustments
Like the ectotherms, endotherms can also use changes in the environment 🌳.
❄️ a) To Cool the Body
Humans and other animals use shades of trees 🌳. The body's response is perspiration 💦:
- Dogs perspire through tongue 🐕👅
- Horses through skin 🐴💦
- Humans through specifically active glands 👨💧
Humans also wear clothes which allow ventilation of heat 👕. In addition, humans have invented fans 🌀 and air conditioners ❄️ to cool themselves 🏠.
🔥 b) To Heat the Body
Through external sources such as:
- Shelter 🏠
- Fire 🔥
- Covering for heat conservation 🧥
- Huddling together in animals (especially young) 🐾 and in humans warm clothing 🧣
- Hot beverages ☕
- High energy providing foods 🍲
- Warm and heated homes (from fire) 🔥🏡
🔥 Heat Production
What does the body do when heat is needed to be generated? 🌡️⬆️
- Increase in the basal metabolism 📈
- Increase in muscular activity 💪
- Shivering 🥶
- Increase in the sympathetic systems ⚡ (increased heart pulse rate ❤️, adrenaline 💉, and thyroid release 🏥)
💨 Heat Loss
Heat needs to be radiated away from the body (from the inside) 🌡️⬇️ one mechanism is evaporation through sweating 💦, and conducting the heat out through other sources 🔄.
Conduction through taking a bath 🛁—dogs 🐕, buffaloes 🐃 and other animals stay in water 💧 during hot days ☀️.
❄️ Response to Cold
Response to cold is constriction of blood vessels in the periphery 🔵 for maintaining the internal core temperature at a constant ⚖️, and reducing loss of heat through radiation (to the outside) 🔥❌. This is why we have cold hands and feet in winter ❄️🤚🦶, and which is why the mountain climbers 🏔️ often lose their fingers and toes because of freezing ⚠️.
Fur bearing animals also respond by pilo erection (raising the fur on their body) 🦁, and birds do it by fluffing their feathers 🦅. The skin sensors important as they also provide information of heat and cold 🌡️📡.
Though behavioral responses like seeking heat when cold 🔥 or taking a bath when hot 💧 are mechanisms for temperature control, the physiological and brain mechanisms take a priority 🧠⚡.
🧠 Brain/Neural Substrates of Thermoregulatory Behavior
🏥 Preoptic Area - Master Control
Preoptic area in the anterior hypothalamus 🏥 is the master control in both heating and cooling mechanisms 🎛️. Heating this area leads to sweating 💦, and cooling it leads to shivering 🥶, both these are body's reaction to thermoregulatory challenges ⚖️.
🦴 Lower Phylogenetic Areas
The lower phylogenetic areas involved in thermoregulation are in the brain stem 🧠 (which are under the hypothalamic control and the spinal cord 🦴, but the range of the spinal neutral zone (about 2-3 degrees) is too wide and therefore primitive (not refined) ⚠️ as the organism can die of:
- Hypothermia ❄️ (cold: freeze)
- Hyperthermia 🔥 (heat: heat stroke)
Before the body starts responding 💀.
The main control of the thermoregulatory remains with anterior/posterior hypothalamus 🏥⚡.
🧪 Biochemical Control
The biochemical control of thermoregulation is with the endorphins (brain opioids) 😌. Injecting endorphins directly into the hypothalamus 💉🏥 leads to an immediate action of lowering the body temperature ⬇️🌡️. Naloxone 💊 (antagonist of opiates) block this endorphin induced lowering of temperature 🛑. WHY? - Because that pain and temperature-sensory systems are related ⚠️🌡️.
🤒 What Happens in Fever?
❓ What is Fever?
Bacteria 🦠 or virus 🦠 produce pyrogens 🔥 which affect the hypothalamic set point of 98.4°F. Temperature rises above the set point of 98.4° (37°C) high temperature damage body cells need to lower temperature inside 🌡️⚠️. Rise in the hypothalamic set point sends out signals to heat up the body 🔥⬆️.
🔄 Normal vs Fever Conditions
Under the Normal conditions ✅, the hypothalamic set point is at 98.4° and the body is also at 98.4° and these both work to maintain the same ⚖️.
In fever 🤒 the temperature regulating systems (anterior hypothalamus and the preoptic area 🏥) bring about changes in the hypothalamic set point. These changes are in response to the attack from pyrogens (from bacteria) 🦠. Thus, the set point moves up to 101°F ⬆️, whereas the body is still functioning at 98.4°F. Urgently signals are sent to the body that there is need to heat up to meet hypothalamic set point 📡, to preserve heat. Thus, there is a response of heat conservation and generation i.e., shivering 🥶, cold hands and feet ❄️🤚🦶 (circulation to the center) and faster metabolism ⚡.
💊 What Happens When We Take Aspirin?
What happens when we take aspirin (antipyretic) 💊, it reduces the set point back to normal 98.4°F ⬇️, whereas now the body has been working at 101°F ⬆️. The signals this time are the body needs cooling! ❄️ So, this is why we see sweating 💦 and taking off blankets etc. when the fever "breaks" 🛏️❌. The signals are to slow metabolism ⬇️, and to radiate heat by evaporation (sweating) 💧.
👥 Human Behavioral Thermoregulation
In human, clothes are the thermoregulatory devices 👕 and the kinds of houses built for the climate we live in is a thermoregulatory behavioral process as well 🏠🌡️. Animal studies have shown that they seek active regulation of their environment i.e., rats hoard paper to warm their cages 🐀📄.
⚠️ Thermoregulatory Limits
Thermoregulatory process is however very limited ⚠️. Because freezing to death ❄️💀 or dying from heat stroke 🔥💀 i.e., hypothermia or hyperthermia occur when the behavioral and physiological regulatory mechanisms cannot cope further 🚫.
📚 References
- Carlson, N. R. (2005). Foundations of physiological psychology. Pearson Education New Zealand.
- Pinel, J. P. (2003). Biopsychology. (5th ed). Allyn & Bacon Singapore.
- Bridgeman, B. (1988). The Biology of Behavior and Mind. John Wiley & Sons, New York
- Mogensen, G. J. (1977). The Neurobiology of Behaviour. Lawrence Elbaum Associates